1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display apparatus used in a color television set or various types of office automation (OA) apparatus, and a manufacturing device for practicing such a method.
2. Description of the Related Art
Liquid crystal display apparatus used in a color television set or an OA apparatus have a structure in which the first polarizing plate made of a glass plate-like material, a color filter plate (the first substrate), a liquid crystal drive plate (the second substrate), the second polarizing plate and a flat-plate backlight are combined and laid one on another in this order from the display surface side.
A liquid crystal cell is manufactured by bonding the above-mentioned color filter plate and liquid crystal driving plate one on another while interposing liquid crystal and spacer between them. When the color filter plate and liquid crystal driving plate are bonded together, a thermosetting sealing agent is applied between the circumferential portions of these plates, and they are bonded with use of a bonding device.
Here, when bonding them together, it is required that the positions of the color filter plate and liquid crystal driving plate with relative to each other should be aligned at a high accuracy.
In the meantime, to meet the demand of increasing the size of the liquid crystal display screen and improving the production efficiency, such a procedure is employed that a plurality of liquid crystal cells (for example, 4 crystal cells of a size of 12 inches) are cut out of a large-scale glass substrate (400 nm×500 nm).
The bonding device has a stand and an XYZθ driving mechanism is provided on the stand. The XYZθ driving mechanism includes a first attraction stage configured to attract an opposing substrate to the stage and hole it in a horizontal state. The opposing substrate contains a plurality of sheets of effective regions that constitute the above-mentioned color filter plate.
On the other hand, a second attraction stage is provided underneath the first attraction stage, and an array substrate is attracted to the second attraction stage and held on it in a horizontal state. The array substrate contains a plurality of sheets of effective regions that constitute the above-mentioned liquid crystal driving plate, and this substrate is set to face the opposing substrate.
Underneath the second attraction stage, there are provided recognition cameras for recognizing alignment marks provided on, for example, four corners of the opposing substrate and the array substrate, and an ultraviolet ray irradiating means for hardening a UV-hardening sealing agent used for preliminary fixation, which will be explained later.
Now, the step of bonding the opposing substrate and the array substrate together will now be described.
First, the thermosetting sealing agent for sealing liquid crystal is applied onto the array substrate in an amount for four liquid crystal cells, and the UV-hardening sealing agent for preliminary fixation is applied onto a vicinity of the alignment mark at each of the four corners of the substrate. Then, the array substrate is attracted and fixed on the first attraction stage. After that, the opposing substrate is attracted to the second attraction stage and held on it to be in parallel to the array substrate. After that, the opposing substrate is moved down so as to bring it into contact with the thermosetting sealing agent and the UV-hardening sealing agent for preliminary fixation, that are provided on the array substrate. Subsequently, the position alignment marks made at the circumferential portions of the opposing substrate and array substrate are aligned with each other while monitoring them with the recognition cameras. At the same time, the opposing substrate is moved down such that the gap between the opposing substrate and array substrate becomes a predetermined distance.
Next, an ultraviolet ray is irradiated onto the preliminary-fixation UV-hardening sealing agent applied on the vicinities of the alignment marks, and thus the opposing substrate and array substrate are preliminary fixed together. The opposing substrate and array substrate that are preliminary fixed together as above are heated in the subsequent step. Thus, the thermosetting sealing agent is hardened and they are adhered together permanently.
However, in the conventional techniques, the opposing substrate and array substrate are aligned with each other while they are brought into contact with each other via the thermosetting sealing agent and UV-hardening sealing agent. In this state, the viscoelastic resistance of each sealing agent is applied to the XYZθ driving mechanism and the second attraction stage, resulting in that some distortion is created in the entire bonding device.
Here, the distortion is proportional to the amount of movement of the opposing substrate, and therefore even if correction is performed on the basis of a correction amount calculated after detection of the displacement amount with use of the recognition cameras, some distortion is still inevitable. For this reason, it is not possible to carry the opposing substrate to the desired position by one movement, but the correction must be repeated many times until the displacement error falls within a generally-accepted allowable range of ±1 μm.
Such operations cause an increase in tact time in the sell assembly step or eventually a decrease in the production efficiency.